This is not due to a change in the Excel Connector, but the IS department changes made, and I am going to guess to a proxy server possibly? They may be able to find what's being blocked in their log files and fix the issue for you. Another thing others said fixed the issue was to change the server URL to http://login.salesforce.com/services/Soap/c/16.0 and make sure your combination of security token and password is correct. I have never done this though, so I can't verify...